In the primary fractionators or oil quench towers of ethylene plants, hot cracked gases from the cracking furnaces are cooled and fractionated to remove fuel oil, pyrolysis gasoline and lighter gases. Unfortunately, the temperatures in the quench oil section lead to the formation of heavy tar molecules via various condensation and polymerization mechanisms. The tar can plug process equipment such as exchangers, trays, etc., as well as reduce the run time of the fractionator column. In addition, coke fines from the cracking furnace may contribute to further heavy fouling in the flow lines and in the tower. In many instances, ethylene plant operators need to inject a lighter stream, such as light cycle oil, into the fractionator bottoms to control tar viscosity in an effort to meet final product specifications. This is always done at great economic expense. All of these problems occur commonly in gas oil crackers that process heavier feedstocks, but may also occasionally appear with lighter feedstocks, especially when increased severity of cracking is applied.
Such problems can be mitigated with specially-formulated antifoulants that will survive high temperatures and inhibit the heavy fouling type components of the quench oil from aggregation and deposition, thus improving the fluid flow characteristics.
Accordingly, it would be desirable to provide an improved method for mitigating fouling and reducing viscosity in the primary fractionators and quench sections of ethylene plants. It would also be desirable to identify a series of additives that will act as fouling inhibitors, tar dispersants and viscosity reducers in cracked hydrocarbon fluids to improve flow characteristics and inhibit precipitation of deposits at high temperatures.